Microwave tube assembly

ABSTRACT

A microwave tube assembly comprising a main collector for trapping electrons passing through the microwave outlet of the high frequency section of a microwave tube where incoming microwaves and the electrons act on each other; a plurality of subcollectors disposed between the microwave outlet and the main collector; and a magnetic shield plate for shutting off a magnetic field acting in the axial direction of the microwave tube wherein said plural subcollectors consist of at least first and second units; at least part of the first subcollector is disposed on the side of the main collector and the second subcollector is placed on that side which faces the microwave outlet; the second subcollector and main collector are maintained at a substantially equal voltage; the first subcollector is held at a higher voltage than the second subcollector; and the magnetic shield plate is disposed in the region where said first subcollector which faces the main collector is arranged.

i s United States ate [151 3,709,963

Shimada 1 Oct. 24, 1972 [541 MICROWAVE TUBE ASSE 13 Primary Examiner-Herman Karl Saalbach 7 t Takashi T k Assistant Examiner-Saxfield Chatmon, Jr. 2] Inven or Shimada, 0 yo Japan Att0mey R D. Flynn et a1. [73] Assignee: Tokyo Shibaura Electric, Ltd,

Kawasaki-shi, Japan [57] CT Filed: July 13, 1971 A microwave tube assembly comprising a main collector for trapping electrons passing through the [21] Appl' 162,206 microwave outlet of the high frequency section of a microwave tube where incoming microwaves and the Foreign Application Priority Data electrons act on each other; a plurality of subcollec- July 16 1970 Japan 45/61766 tors disposed between the microwave outlet and the main collector; and a magnetic shield plate for Oct. 6, 1970 Japan ..45/98807 Shutting off a magnetic field acting in the axial direction of the microwave tube wherein said plural (g1 MS/Sisal?i subcollectors consist of at least first and second units; [58] Fie'ld 5/5 38 3 5 at least part of the first subcollector is disposed on the side of the main collector and the second subcollector is placed on that side which faces the microwave out- [56] References Cited let; the second subcollector and main collector are UNITED STATES PATENTS maintained at a substantially equal voltage; the first subcollector is held at a higher voltage than the 3,394,282 7/ 1968 Schmidt ..315/5.38 Sacond subcollector; the magnetic Shield plate is y ggg 'i s disposed in the region where said first subcollector o a h' M" th 011 t (1. 3,453,482 7/1969 Preist ..315/5.38 x we ia???M92395---?5-9535r995-- 3,172,004 3/1965 Von Gutfeld 6 3m 3 11 Figures -,3 553i X, 3,188,515 6/1965 Kompfner ..315/5.38 3,271,618 9/1966 Kooyers ..3l5/5.38 X

' IL 7 3 E2 E3 2a 2b 2c 2o ,j I5 E1 L- I 8 9a 4o 4 4 4 so '13 i5 10 PATENTED 0m 24 I972 SHEET 1 0F 3 FIG? FEG.3

PATENIED 3.700.963

sum 2 or 3 FIG. 4 FIG. 5

FIGS

VII

MICROWAVE TUBE ASSEMBLY This invention relates to a microwave tube having collectors for trapping electrons passing through the microwave outlet of the high frequency section of said tube where incoming microwaves and the electrons act on eachother and more particularly to a microwave tube assembly which is provided with means for preventing secondary electrons from proceeding to the high frequency section of the tube.

Microwave tubes to which this invention can be effectively applied typically include a klystron and a travelling wave tube where electron beam is made to proceed linearly.

The high frequency section of a klystron, for example, of a type permitting the linear movement of electrons has a microwave input cavity at one end, a microwave output cavity at the opposite end and generally an intermediate cavity therebetween, all these cavities being connected by drift tubes. In the side of saidinput cavity is disposed an electron gun for causing electrons to proceed to form electron beam along the axis of the high frequency section, and in the side of said output cavity are placed a main collector for trapping the electrons which have left the high frequency section. The electrons are modulated in velocity by high frequency input signals conducted into the microwave input cavity and further modulated in density while travelling through the intermediate cavity and drift tubes. When the electrons whose density has been modulated pass through the output cavity, there are drawn out'therefrom amplified microwaves. The electrons leaving said output cavity are trapped by the main collector.

The input power supplied to such microwave tube is determined by a product arrived at by multiplying the electron beam current by the value of voltage impressed on the main collector. The overall efficiency of the microwave tube is expressed in the ratio which the high frequency energy drawn out of the output cavity bears to the input power. To elevate said overall efficiency, therefore, it is necessary to reduce the voltage of the main collector. Improvement in said overall efficiency is strongly demanded from the standpoint of saving power-consumption in operating a microwave tube and reducingthe cost of power source equipment.

When the electrons which have served the purpose are trapped by the collectors, there are emitted secondary electrons from the main collectors due to the impingement thereon of the first mentioned electrons. As the main collector is used at a lower level of voltage than that of the other sections of a microwave tube, for example, the drift tubes, the secondary electrons are likely to intrude into the high frequency section in a more accelerated state, thus obstructing amplification and oscillation of microwaves.

It is accordingly the object of this invention to provide a microwave tube assembly wherein the collector construction is so improved as to prevent the aforesaid secondary electrons from being carried into the high frequency section of said tube.

microwaves and electrons passing therethrough act on each other, one end of which constitutes a microwave inlet and the opposite end of which constitutes a microwave outlet; electron beam generating means connected to the microwave inlet so as to supply the electrons; means for generating a magnetic field acting in the axial directions of the microwave tube so as to converge said electrons; a main collector for trapping the electrons leaving the high frequency section; a plurality of subcollectors disposed between the microwave outlet and the main collector; and a magnetic shield plate for shutting off the magnetic field acting in the axial direction of the microwave tube, wherein the plural subcollectors consist of at least first and second units; at least part of the first subcollector is disposed on that side of the microwave tube which faces the main collector; the second subcollector is placed on that side of the microwave tube which faces the microwave outlet and is maintained at substantially the same voltage as the main collector; the first subcollector is held at a higher voltage than the second subcollector; and the magnetic shield plate is disposed in the region where the first subcollector which faces the main collector is arranged,

The main features of this invention are that while secondary electrons from the main collector proceed to the first subcollector having a higher voltage than the main collector, they are decelerated at the second sub- I collector having a lower voltage than the first subcollector to be prevented from being conducted to the high frequency section; and that secondary electrons proceeding through that nonmagnetized section which is created due to the sudden shut off of a magnetic field are made to rotate rapidly in the magnetized area of the subcollector section to be prevented from further travelling to the high frequency section.

The shape and position of the subcollector and the position of the magnetic shield plate may be suitably varied. If there is further provided a third subcollector, the intrusion of secondary electrons into the high frequency section of the microwave tube will be obstructed more effectively.

This invention can be more fully understood from the following detailed description when taken in connection with the accompanying drawings, in which:

FIG. 1 is a cross sectional view of a klystron according to an embodiment of this invention, showing the voltage relationship of the main parts thereof;

FIG. 2 is an enlarged sectional view of the subcollector section of FIG. 1, illustrating an electric field formed therein;

FIG. 3 shows the manner in which a magnetic field acting in the axial direction of the microwave tube is distributed through the subcollector section of FIG. 2;

FIG. 4 is a sectional view of the magnetic shield plate of FIG. 2 disposed at a different place according to another embodiment of the invention;

FIG. 5 is an enlarged sectional view of the subcollector of FIG. 1 modified according to another embodiment of the invention;

FIG. 6 is an enlarged sectional view of the subcollector of FIG. 1 modified according to still another embodiment of the invention;

FIG. 7 is a sectional view on line VII-VII of FIG. 6; and

FIG. 8 is an enlarged sectional view of the subcollector of FIG. 1 modified according to a further embodiment of the invention.

klystron comprises a microwave inlet resonance cavity 2a into which there is inserted a high frequency signal input conductor 1; a microwave outlet resonance cavity 2e into which'there is fitted a high frequency signal output conductor 3; a plurality of cavities 2b to 2d disposed between said resonance cavities 2a and 2e; a plurality of drift tubes 4a to 4d connecting said cavities with each other; a magnetic field generator 6 for generating a magnetic field acting in the axial direction of the microwave tube so as to converge electrons passing through the drift tubes 4a to 4d; and a magnetic shield casing 7 for shielding the high frequency section magnetically. Numeral 8 is an electron gun which emits a beam of electrons and also includes means for accelerating said electrons. The electron gun 8 supplies a beam of electrons to the high frequency section through a tube 9a and has its filament supplied with current by a power source E. A tube 9b opened to the microwave output cavity 2e has a flange 90 which faces the opening of the main collector 10 for trapping electrons 5. Between the main collector 10 and the flange 9c is disposed a group of subcollectors consisting of a first annular subcollector 12, a second subcollector 13 and a third subcollector 14 with a vacuum insulation ring 15 inserted between the adjacent ones of said first to third subcollectors 12, 13 and 14, between said group of subcollectors and the main collector 10 and between said group of subcollectors and the flange 9c. The arrangement of these main collector and subcol lectors and vacuum insulation rings is presented in enlargement in FIG. 2. The annular magnetic shield plate 11 has a portion around its central opening embedded in the first supplementary collector 12 and is extended outward to have the periphery connected to the magnetic shield casing 7 through an insulating material 16.

The negative pole of the power source E is connected to the power, source E and the positive pole of the power source E is connected to the magnetic shield casing 7. A voltage between the power sources E and E is supplied through a line 18 to the main collector 10 and the second subcollector 13. A higher voltage than that of the main collector 10 is impressed on the first subcollector 12 and third subcollector 14 through a voltage dividing resistor 19 and line 20. In some cases the line 20 is directly connected to the positive pole of the power source E It will be apparent that the voltage relationship of the main collector and subcollectors is indicated simply for illustration and that this invention is not limited to this embodiment. The point is that the second subcollector 13 should have substantially the same voltage as the main collector l0 and that the first and third subcollectors 12 and 14 should have a higher voltage than the second subcollector 13.

Now let it be assumed that under. the aforesaid arrangement, the first and third subcollectors l2 and 14 are impressed with the same voltage as that supplied to the drift tubes 4 and that the main collector 10 and the second subcollector 13 are supplied with a lower voltage than that of said drift tubes 4. Then there appears in a group of all collectors including the main collector 10 a potential distribution or an equipotential plane indicated in broken lines in FIG. 2. Accordingly, secondary electrons proceeding from the main collector 10 toward the high frequency section receive a force acting in the direction of the arrows 22. When secondary electrons are drawn near the second subcollector 13,

they are decelerated and slowed down to substantially the same velocity as that at which they are emitted at the interior of the main collector 10. The secondary electrons thus decelerated are attracted by the electric field of the first subcollector to be effectively trapped thereby.

Yet, some portions of said secondary electrons are most likely to proceed to the high frequency section of the microwave tube. If the voltage of the second subcollector 13 was made further lower than that of the main collector 10, then secondary electrons could be fully trapped by either the main collector 10 or the first subcollector 12, thereby preventing them from entering the high frequency section. From the standpoint of effecting perfect insulation, however, it is not desirable to construct a microwave tube so as to obtain, the above-mentioned voltage relationship 'of both types of collectors.

According to this invention, therefore, there is provided the magnetic shield plate 11 for the subcollector section so as to subject secondary electrons to the same treatment as that which would be effected by reducing the voltage of the second subcollector 13 to a far lower level than that of the main collector 10.

A magnetic field 23 0n the axis of the microwave tube is sharply shut off, as shown in FIG. 3, around a point 1 1:: corresponding to the position of the magnetic shield plate 11. Secondary electrons advancing from the main collector 10 toward the high frequency section are conducted to the magnetic field 23 and made to rotate rapidly about the axis of the microwave tube. As a result, the velocity at which the secondary electrons proceed in the axial direction of the microwave tube is reduced to an extent equal to that amount of energy which is consumed in said rotation, 50 that the secondary electrons lose a sufficient velocity to reach the high frequency section before they are brought to a region where there prevails a potential approaching that of the second subcollector 13. Further, the secondary electrons in the direction of high frequency section thus slowed down are accelerated by a strong electric field generated by the first subcollector 12 to be retracted away from the high frequency section and eventually trapped by either said first subcollector 12 or main collector 10.

With the magnetic field 23 taken to have 300 gauss, secondary electrons advancing toward the second subcollector 13 are supplied with a rotating velocity corresponding to about 2000 V due to the sudden broadening of a magnetic field in the region of the first subcollector 12. This subjects the secondary electrons to the same treatment as that which would be effected by decreasing the voltage of the second subcollector 13, 2000 V from that of the main collector 10.

Secondary electrons travelling toward the high frequency section along an orbit very close to the axis of the microwave tube do not have a great rotating energy. If, however, the axes of the respective subcollectors are slightly displaced from each other, then even such secondary electrons can be captured.

When secondary electrons are made to rotate as described above, they can be treated in the same manner as if the voltage of the second subcollector 13 was appreciably decreased from that of the main collector 10, though the voltages of both collectors l0 and 13 are actually made substantially equal. This enables the voltage of the main collector to be reduced to a far lower level than that of the high frequency section, thus providing a high performance microwave tube.

The magnetic shield plate 11 may be disposed anywhere in an area defined between the first and third subcollectors l2 and 14. Or said plate 11 may be so located as to abut on the outer peripheral walls of any of said subcollectors. FIG. 4 shows the magnetic shield plate 11 fitted to the peripheral walls of the first subcollector 12. Or, the second subcollector 13 may be positioned close to the flange 90, as illustrated FIG. 5,

without providing the third subcollector 14.

As shown in FIG. 1, the second subcollector 13 is maintained at a negative high voltage with respect to the magnetic shield casing 7, so that it is obviously safe to prevent said second subcollector 13 from being exposed and it is advisable to use as small a number as possible of insulation rings 15 from the standpoint of avoiding the leakage of microwaves through an insulating material.

FIG. 6 indicates the arrangement-of a collector assembly capable of preventing the exposure of the second subcollector 13 and reducing the number of places where there is provided an insulating material. The same parts of FIG. 6 as those of the foregoing embodiments are denoted by the same numerals and description thereof is omitted. That part of the first subcollector 12a which faces the microwave outlet has a larger inner diameter 25 than the inner diameter 26 of that part of said subcollector 12a which faces the main' collector 1.0. The magnetic shield plate 11 directly abuts on that side of said subcollector 12a which faces the main collector 10. The second subcollector 13a is disposed concentrically with the axis of microwave tube in that cavity of the first subcollector 12a which has said larger inner diameter 25. A plurality of support members 27 are arranged parallel and concentrically with the axis of the microwave tube and fitted at one end to the main collector 10. These support members 27 are extended through the apertures 28 and 29 formed in the magnetic shield plate 11 and the first subcollector 12a so as to support the second subcollector 13a. Accordingly it is possible not only to prevent the second subcollector 13a from being exposed outside of the microwave tube, but also to eliminate the necessity of using an insulation ring for fitting the second subcollector 13a. The support members 27 play the part of maintaining the second subcollector 13a and main collector 10 at the same voltage as well as of transmitting to the main collector 10 the heat generated by power loss in the subcollector 13a.

Referring to FIG. 1, power consumed in the first subcollector 12a is expressed in a product arrived at by multiplying the current of secondary electrons by the voltage of the main collector 10. Therefore, the more decreased the voltage of the main collector 10, the more increased power loss in the first subcollector 12a. This would not only reduce the overall efficiency of a microwave tube, but also in the case of a large power microwave tube, make it necessary to provide cooling means for the first subcollector 12a.

FIG. 8 shows another embodiment of this invention comprising means for preventing the overheating of the first subcollector. Referring to FIG. 8, the first subcollector 12b has the same structure as if the first and third subcollectors l2 and 14 of FIG. 2 were integrated into one body. That part of said first subcollector 12b which faces the main collector 10 has a larger inner diameter 30 than the inner diameter 31 of that part of said subcollector 1212 which faces the microwave outlet. The magnetic shield plate 11 is disposed close to that part of the first subcollector 12b which faces the main collector 10. The second subcollector 13b is placed in that cavity of the first subcollector 12b which has said larger diameter 30, and supported, as in FIG. 6, by a plurality of support members 27 extended from the main collector 10 through the magnetic shield plate 11. The third subcollector 14b has its cylindrical walls formed of a meshed metal screen and concentrically disposed with the axis of the microwave tube. Said third subcollector 14b is fixed at one end to the periphery of the central opening of the magnetic shield plate 11 and so placed as to cover the inner peripheral walls of the right half, as indicated, of the second subcollector 13b.

In the embodiment of FIG. 8, secondary electrons emitted from the inner walls of the main collector 10 are mostly brought into the third collector 14b. Almost all these secondary electrons pass through the meshes of the third subcollector 14b to the second subcollector 13b and trapped by the electrode of said second subcollector 13b. Since secondary electrons have little energy when they are captured by the second subcollector 13b after passing through the mesh of the third subcollector 14b, said second subcollector 13b is little heated, nor is the first subcollector 12b, thus eliminating the necessity of providing any extra cooling means. The magnetic shield plate 11 of FIG. 8 has the same efiect as that of FIG. 1.

The shape of plural subcollectors used in a microwave tube according to this invention is not limited to those described in the preceding embodiments, but any modification thereof is included in the invention, provided it does not depart from the object and scope of the invention.

What we claim is:

l. A microwave tube assembly comprising a high frequency section where incoming microwaves and electrons travelling through said tube act on each other, one end of which constitutes a microwave inlet, and the opposite end of which constitutes a microwave outlet; means connected to the microwave inlet for supplying electrons; means for generating a magnetic field acting in the axial direction of the microwave tube so as to converge the supplied electrons; a main collector for trapping the electrons which have left the high frequency section; a plurality of subcollectors arranged in order and adjacent each other between the microwave outlet and the main collector; and a magnetic shield plate for shutting ofi a magnetic field acting in the axial direction of the microwave tube, said plural subcollectors comprising at least first and second subcollectors, at least part of said first subcollector being disposed on that side of the microwave tube which faces the main collector and said subcollector being placed on that side of said tube which faces the microwave outlet; the second subcollector being maintained at substantially the same level of voltage as the main collector; the first subcollector being maintained at a higher voltage than the second subcollector; and the magnetic shield plate being disposed in the region where said first subcollector which faces the main collector is arranged.

2. A microwave tube assembly according to claim 1 wherein the plural subcollectors include a third subcollector which is located between that side of the microwave tube which faces the microwave outlet and the second subcollector, said third subcollector being impressed with a higher voltage than that supplied to the main collector.

3. A microwave tube assembly according to claim 2 wherein the first and third subcollectors are impressed with the same level of voltage.

4. A microwave tube assembly according to claim 1 wherein that part of the first subcollector which faces the microwave outlet has a larger inner diameter than that part of said subcollector which faces the main collector; the magnetic shield plate is so disposed as to abut against that part of the first subcollector which faces the main collector; and the second subcollector is positioned in that cavity of the first subcollector which has said larger inner diameter and supported by a plurality of support members which are insulated from the first subcollector and magnetic shield plate and so extended as to electrically and mechanically connect the second subcollector to the main collector. I

5. A microwave tube assembly according to claim 4 wherein there is further provided a third subcollector between that part of the microwave tube which faces the microwave outlet and the second subcollector which is impressed .with a higher voltage than that supplied to the main collector.

6. A microwave tube assembly according to claim 1 wherein that part of the first subcollector which faces the main collector has a larger inner diameter than the inner diameter of thatpart of said subcollector which faces the microwave outlet; the magnetic shield plate is so positioned as to abut against that part of the first subcollector which faces the main collector; the second subcollector is disposed in that cavity of the first subcollector which has said larger inner diameter and 'supported by a plurality of supports insulated from the magnetic shield plate and so extended as to electrically and mechanically connect the second subcollector to the main collector; and the plural subcollectors include a third subcollector which has cylindrical meshed walls and is fitted at one end to the periphery of the central opening of the magnetic shield plate for mechanical and electrical connection, so as to cover part of the inner peripheral walls of the second subcollector. 

1. A microwave tube assembly comprising a high frequency section where incoming microwaves and electrons travelling through said tube act on each other, one end of which constitutes a microwave inlet, and the opposite end of which constitutes a microwave outlet; means connected to the microwave inlet for supplying electrons; means for generating a magnetic field acting in the axial direction of the microwave tube so as to converge the supplied electrons; a main collector for trapping the electrons which have left the high frequency section; a plurality of subcollectors arranged in order and adjacent each other between the microwave outlet and the main collector; and a magnetic shield plate for shutting off a magnetic field acting in the axial direction of the microwave tube, said plural subcollectors comprising at least first and second subcollectors, at least part of said first subcollector being disposed on that side of the microwave tube which faces the main collector and said subcollector being placed on that side of said tube which faces the microwave outlet; the second subcollector being maintained at substantially the same level of voltage as the main collector; the first subcollector being maintained at a higher voltage than the second subcollector; and the magnetic shield plate being disposed in the region where said first subcollector which faces the main collector is arranged.
 2. A microwave tube assembly according to claim 1 wherein the plural subcollectors include a third subcollector which is located between that side of the microwave tube which faces the microwave outlet and the second subcollector, said third subcollector being impressed with a higher voltage than that supplied to the main collector.
 3. A microwave tube assembly according to claim 2 wherein the first and third subcollectors are impressed with the same level of voltage.
 4. A microwave tube assembly according to claim 1 wherein that part of the first subcollector which faces the microwave outlet has a larger inner diameter than that part of said subcollector which faces the main collector; the magnetic shield plate is so disposed as to abut against that part of the first subcollector which faces the main collector; and the second subcollector is positioned in that cavity of the first subcollector which has said larger inner diameter and supported by a plurality of support members which are insulated from the first subcollector and magnetic shield plate and so extended as to electrically and mechanically connect the second subcollector to the main collector.
 5. A microwave tube assembly according to claim 4 wherein there is further provided a third subcollector between that part of the microwave tube which faces the microwave outlet and the second subcollector which is impressed with a higher voltage than that supplied to The main collector.
 6. A microwave tube assembly according to claim 1 wherein that part of the first subcollector which faces the main collector has a larger inner diameter than the inner diameter of that part of said subcollector which faces the microwave outlet; the magnetic shield plate is so positioned as to abut against that part of the first subcollector which faces the main collector; the second subcollector is disposed in that cavity of the first subcollector which has said larger inner diameter and supported by a plurality of supports insulated from the magnetic shield plate and so extended as to electrically and mechanically connect the second subcollector to the main collector; and the plural subcollectors include a third subcollector which has cylindrical meshed walls and is fitted at one end to the periphery of the central opening of the magnetic shield plate for mechanical and electrical connection, so as to cover part of the inner peripheral walls of the second subcollector. 